This invention relates to improvements in methods of and in apparatus for treating tows of fibrous filter material for tobacco smoke, and more particularly to the treatment of filter tows on their way from a source (such as a bale) to one or more stations where the treated tow is draped into a web of suitable wrapping material and the thus obtained filter rod is subdivided into filter rod sections of unit length or multiple unit length. Such filter rod sections can be transported to storage or into the magazine(s) of one or more filter tipping machines wherein the sections are united with plain cigarettes, cigars, cigarillos or other rod-shaped tobacco-containing products to form therewith filter cigarettes, cigars, cigarillos or other filter tipped smokers' products.
It is customary to convey an elongated tow of filter material for tobacco smoke along an elongated path wherein the cross-sectional area of the tow is gradually reduced to that of the rod-like filler of a filter rod, and the thus obtained rod-shaped intermediate product is draped into a continuous web of cigarette paper, artificial cork or other suitable wrapping material to form with the finished wrapper a continuous filter rod. It is also customary to introduce into successive increments of the running tow a suitable fluid, such as compressed air, and to permit or cause the fluid to escape from the tow at a location ahead of the wrapping station. Reference may be had, for example, to the so-called AF filter rod production line which is distributed by the assignee of the present application.
The path wherein the cross-sectional area of the running tow is being reduced is defined, at least in part, by an elongated channel surrounding an elongated passage of diminishing cross-sectional area (as seen in the direction of advancement of the tow toward the wrapping (filter rod forming) and rod subdividing stations. The fluid (normally but not necessarily compressed air) is introduced into the passage by way of a first set of openings, and a second set of openings in the channel serves to permit or effect the evacuation of fluid from the passage for the filter tow.
In addition to or in lieu of compressed air, the tow can be acted upon by carbon dioxide gas and/or steam. The tow normally consists of crimped filamentary synthetic filter material, such as cellulose acetate or the like. The term channel is intended to denote that part of the filter rod making machine or production line which is often called finger and constitutes an elongated tube defining a passage having a cross-sectional area which diminishes in the direction of advancement of successive increments of an elongated filter tow therethrough. As a rule, the cross-sectional area of the passage at the outlet of the channel or finger equals or approximates the cross-sectional area of the rod-like filler (compacted or condensed filter tow) which is ready to be draped into cigarette paper or the like.
A standard apparatus for processing tows of filter material for tobacco smoke is disclosed, for example, in U.S. Pat. No. 5,106,357 granted Apr. 21, 1992 to Kampen for "METHOD AND APPARATUS FOR PRODUCING TOBACCO SMOKE FILTER RODS". This patent discloses the introduction of compressed air into the channel or finger for the purpose of enhancing the homogeneity of the tow, and the thus admitted air is thereupon caused or permitted to escape through the interstices of a substantially sieve-like portion of the channel. It has been found that such treatment of the tow does not invariably result in the making of a high-quality filter for tobacco smoke.